Whether you are running a meeting or you are alone and want to ensure that you are considering everything relevant, what you do is set up a sequence of hats, such as blue -- red -- yellow -- black -- white -- green -- red -- blue, and then (get everyone to) put on each hat in the sequence and try to produce thoughts of that kind. In a meeting you invite all the participants to put on the same hat at the same time. If two contradictory thoughts pop up under the same hat, that's fine: both of them are put down in parallel and the contradiction is resolved later. At the end of the sequence you should have a balanced set of information that you can base a decision on.
Some things the six hats are not:

They are not classifications for thoughts which have already occurred. Rather, they are directions in which you should intend to think. You should set out to produce thoughts that will go under a specific hat; you put on your WhiteHat and produce some factual thoughts, then you put on your RedHat and produce some emotional thoughts, and so forth. You do not do some random thinking and then say, "Ah, I see that that was YellowHat thinking." (This is why using the hats as Wiki tags or WikiBadges, on already-written information, is a bad idea. A good idea, though, might be SixThinkingHatsOnaWikiPage.)

They are not classifications for people. While it may be that some people prefer certain kinds of hats, it is not a good idea to attach that person to that hat. The whole value of the SixThinkingHats is that each person learns to think with all of them (one at a time) and thus gets a more balanced view.

They are not "dramatic identities" or characters in a play. In a SixThinkingHats discussion, everybody wears the same hat at the same time. For example, everybody may start with the white hat, then everybody will switch to the red hat, then everybody will switch to the blue hat. It is not correct to assign one person to be the blue hat, and another to be the red hat, and set up a debate. The whole point of the six thinking hats is to allow a discussion where all points of view are considered -- while debate is eliminated entirely! (In a debate, the participants have a tendency to entrench their own positions rather than exploring the opponent's point of view.) This also implies that, in SixThinkingHatsOnaWikiPage, each hat will have its own section on the page, and people will add in their thoughts under that hat -- rather than, e.g., the mess on WhyWeHateLisp.

What the hat metaphor does:

It better separates fact from opinion,

It more easily identifies important parts of the decision making process,

It provides a neutral language for meta-discussion. You can say, "Take off your BlackHat for a moment and look at the upside." The idea is not that BlackHat is wrong, but that it is not the appropriate hat here. All the hats are equally valuable.

It prevents arguments by keeping everybody under the same hat at the same time, and putting down contradictory ideas in parallel, and

It provides a discipline to ensure that the issue under consideration is seen from many sides (e.g., from the points of view of all six hats).

There are many occasions where wearing a black hat can be useful. When an engineer in Chernobyl said "let's see if we can keep the reactor cooling working by the inertia of the generator during a shutdown", someone with a black hat would have had a very useful contribution to make....

Use dramatic signatures like "-- BlackHat" and any new user can click over and see what it means.

How can one remember which color goes with which heading? The book provides some metaphors as memory aids.

I love the concept, and many/most of the colors seem intuitive to me, but I disagree with the choices of white and yellow. I would think white would correspond to "up-side," optimistic, the best that could happen. I think maybe gray would be best to represent "just the facts," unemotional. I also can think of other roles/modes, such as pragmatic (thinking about details, implementation) (brown hat?); tangential, "sideways" thinking (making connections with other issues, concepts, ideas) (possibly related to green hat) (purple hat?)...
This seems double-edged to me. Clearly the idea is that talking about hats encourages people to disengage themselves from their arguments ("this isn't me speaking, it's my BlackHat") and that this is a Good Thing. But isn't it also likely to be a tool for devaluing and trivialising people's opinions or feelings ("what you're saying is just your BlackHat talking, and we don't need to take it seriously because we can just ask you to TakeOffTheHat? instead") ? This SixHats? business seems to deny the fact that some opinions are, rightly, more than hat-deep.

The suggested use of the 'Thinking Hats' is:

to encourage people to use more 'hat's than they normally do

to defer inappropriate modes of thought to a more appropriate moment in the discussion

and not to eliminate them

-- GRLove 2001-07-10

To which, the obvious response is "Now take off your BlackHat and see it more clearly". Bah, humbug!

A different approach is to ask the question "which hat are you wearing now?"
In a neutral way, it invites people to reflect on their perspective.
The other part of answering Gareth is that all hats are considered valuable and contribute to the exploration of an issue. Until you have worn all of the hats (except possibly the BlueHat) your exploration is incomplete. The BlackHat is about logical, rational negatives (as in the DevilsAdvocate position), emotions and feelings come from under the RedHat.

The role of the BlueHat is to ensure that all other hats have contributed equally and that the group is not ignoring one or more of the other hats. This is very useful, because it's easy to get stuck always wearing just one or two hats all of the time. --PeteMcBreenBut isn't it also likely to be a tool for devaluing and trivialising people's opinions or feelings ("what you're saying is just your BlackHat talking, and we don't need to take it seriously because we can just ask you to Take Off The Hat instead") ?

Is this really a problem? As I understand the moral of the SixThinkingHats, it's: "When undertaking a difficult or momentous decision, think about one of these topics at a time. Don't let one category of search interrupt another. When it's all done, you'll have examined your options thoroughly, considered every relevant factor within your knowledge, and can see the picture well enough to make an intelligent, informed decision." Does this carry much danger of disparaging ideas because of the category they fall under? Or perhaps this moral needs to be stated more clearly? -- BenKovitz
I have seen a closely-related thing happen. I know a team whose leadership want everything to be stated positively. You can't say "we aren't going to make this date" - that's bad energy, and the statement is too often just rejected on the basis of form. The result, sometimes, is lost information and a feeling of repression. It doesn't have to happen, but it can happen. And that's not my Black Hat, that's a pure White Hat observation. -- RonJeffries

When you hear whitewashing, you hear dishonesty. When a manager insists on it, it tells the team, "When you work for me, you'd better speak very carefully, because anyone who says anything I don't agree with is gonna get smacked." This dishonesty is quite appropriate in social settings, where no one is relying on you for accurate reports (if your butt looks fat, do you really want to know?). But a business exists to get things done, so you'd better be able to talk clearly about what's going on, good or bad. -- BenKovitz

Why doesn't the PointyHairedBoss just stick his fingers in his ears and yell "na-na-na; I can't hear you!"? Wouldn't it be more honest?

"Project Announcement:
I have news -- great news! (the only kind of news allowed on this project ;-) I have good reason to believe that this project's results will successfully be delivered -- several months after the current planned delivery date. I'm just so happy to be the bearer of such good news!"

But that is the opposite of the SixThinkingHats approach - if you are doing it right then it should ensure that the negative BlackHat views are stated openly without being condemned as 'bad energy'. -- DaveKirbyMarking pages with Hats as categorizing

Identifying and marking wiki contributions with a hat-property can be discussed more generally in:

Sometimes there is apparently only one option, or two (do it or don't do it). In that case, the plan is much simpler.
Did you know

The thing no one ever mentions about this is that Edward Debono has an undisclosed number of shares in a hat company. -- LeonBambrick

That these terms have also passed on into the hacker heritage with slightly different meanings, or perhaps its just the people I encounter...

No, there's a big problem with at least three of the hats being overloaded terms these days. Maybe it's because I do a lot of security work, but when I see WhiteHat and BlackHat, I can not shake the hacker overtones that those terms have adopted. This makes the hats metaphor a lot less useful for me, because my preconceptions of the terms influences the way I think about them. Similarly, RedHat just makes me think of Linux. -- CharlesMillerMetaphors and Concepts

I think there is a conceptual error in some of the assumptions discussed here. The SixThinkingHats metaphor is used to get all the dimensions of a participant's mind and thinking. Human beings tend to have more than one face, but they expose only one at a given moment. The SixThinkingHats system tries to expose the other faces by disconnecting the person from the comment, allowing more detailed input on some discussion. Ridiculing someone's 'HatThoughts?' is not a bad practice, but is instead a sign of the immaturity of the offender and should be eliminated from any discussions. Discussions, workshops, and reviews are meant to improve and help to address the needs of the team, not to find ScapeGoats. -- EnriqueCombaRiepenhausen?
At the risk of outing myself as a geek the whole six hat concept reminds me of a ST:TNG episode titled "Loud As A Whisper". In it a deaf diplomat communicates by means of a "chorus" or group of telepaths who each express a different facet of his personality(one for emotion and creativity, one for reasoned argument etc)... but I digress.